A wide variety of imaging systems have been developed and are presently in use in the medical field. The systems may be generally categorized in a series of “modalities,” with each modality being characterized by its particular physics, control, utility, and so forth. For example, magnetic resonance imaging (MRI) systems are commonly employed for producing images of gyromagnetic material within a subject of interest. Over recent years, such systems have become particularly refined in producing high quality and reliable images of internal organs and other particular types of tissue, in various orientations within the subject. X-ray-based techniques have also grown considerably from their initial roots in analog systems utilizing photographic film. Modem x-ray-based modalities include digital x-ray systems which produce electronic data sets representative of picture elements or pixels within an array that can be reconstructed into a useful and high quality image. Other x-ray-based techniques include computed tomography (CT) systems in which x-ray radiation traverses a subject, impacts a detector, and resulting signals are reconstructed by a computer into a useful image through the subject. Still other modalities include positron emission tomography (PET), ultrasound, and so forth.
While the various modalities of imaging systems used in the medical field have improved dramatically in recent years, and continue to improve, they have tended to develop in isolation. MRI systems, for example, are typically used for specific purposes, such as imaging soft tissues. X-ray-based modalities are often used in other situations for which MRI systems are less suitable. In such systems, where images are desired of tissues or anatomies which cannot normally be identified or contrasted from neighboring structures, various approaches may be employed to provide the desired contrast, typically through the use of liquid contrast agents which are injected into the patient prior to the examination sequence. These contrast agents, however, do not necessarily provide the particular tissue identification desired, may not be retained for the time and in the locations desired for the entire procedure, and may cause complications for certain patients. Other techniques have been developed to attempt to identify probes, catheters, and the like, through the use of one or another modality system. Such probes, for example, may include coils which respond to the pulse sequences of MRI systems, to provide feedback to a surgeon during a surgical intervention such as catheterization, and so forth.
In certain procedures, it would be useful to provide additional feedback to medical personnel of the state of tissues and anatomies based upon a combination of imaging modalities. For example, during catheterization, angioplasty, and similar procedures, MRI systems may permit a surgeon to identify soft tissues through which a probe is inserted, but are not necessarily well suited to imaging tissues indicative of the actual location of the probe. Because surgical interventions happen in real time, currently available technologies for separate modality imaging are simply ill suited to providing this type of information and feedback. There is a need, therefore, for an improved technique for supplying anatomical images to medical professionals which overcomes the limitations of separate modalities such as MRI and x-ray-based systems.